A model system for the study of carcinogenesis in the rat esophagus has been developed. Explants of rat esophagus have been cultured in a chemically defined medium for a period of 50 days. Using immunoperoxidase techniques, rat esophageal keratin can be stained with antibody to mouse skin keratin thus providing an immunological marker of epithelial cell differentiation. The metabolism of a series of N-nitrosamine carcinogens is being investigated in rat esophagus. It is anticipated that this model system will be useful for investigations of chemical carcinogenesis in the rat esophagus.